A) Field of the Invention
The present invention relates to a ZnO-containing semiconductor layer and a ZnO-containing semiconductor light emitting device, and more particularly to a ZnO-containing semiconductor layer and a ZnO-containing semiconductor light emitting device, capable of emitting visual light. Semiconductor which contains ZnO and has the same crystalline structure as that of ZnO is called ZnO-containing semiconductor.
B) Description of the Related Art
Zinc oxide (ZnO) is direct transition type semiconductor having a band gap of 3.37 eV at a room temperature and an exciton binding energy of 60 meV higher than that of other semiconductors, and is expected as high efficiency light emission material. As a portion of Zn is substituted with Mg, a band gap becomes large.
An inter-band transition energy of ZnO is equivalent to an emission energy in an ultraviolet range at a wavelength of 370 nm This wavelength is shorter than a visual light range not shorter than 400 nm having particularly a high value of industrial applications.
Research on narrowing a band gap of ZnO (gap narrowing) has been made in order to realize emission at a wavelength longer than 400 nm.
S. Merita, T. Kramer, B. Mogwitz, B. Franz, A. Polity and B. K. Meyer, phys. stat. sol. (c)3, No. 4, 960-963 (2006) have reported a change in a band gap of mixed crystal obtained by substituting O of ZnO with an element of group VI, specifically, with sulfur (S) or selenium (Se). As shown in FIG. 14, mixed crystals of ZnO1-xSx and ZnO1-xSex show band bowing. Narrow gap can be realized by substituting O with S or Se.
It has been desired to develop ZnO-containing semiconductor material suitable for visual light emission.